Dispensers for liquid materials which employ a wick in order to conduct the liquid material from a reservoir which is isolated from the atmosphere to an evaporating surface which is exposed to the atmosphere have long been known to the art. However, those skilled in the art have not previously taught that in such dispensers the amount of liquid material exposed to the atmosphere outside the dispenser at a given time should be minimized, while the area of the evaporative surface of the wick should be maximized. Thus, while the basic prior art dispenser construction may suffice for the diffusion of fluids which comprise a single component, or an azeotropic mixture of materials which evaporate uniformly, several problems have been noted in the art which prevent the prior art devices from realizing the goal of uniform diffusion over a long period of time when the liquid material to be diffused is a multi-component liquid. This problem is particularly noted in the perfume art, in which multi-component liquids are commonly used.
A major problem with dispensers of the prior art, when used to dispense liquids having multiple components of differing volatility, is that the material dispensed at a given time changes in amount and character during the life of the dispenser. This result is obtained because when the liquid material to be dispensed is exposed to air, the more volatile constituents of the liquid material rapidly evaporate and become depleted while the dispenser is in use, so that in the early stages of operation the dispenser diffuses a material which is rich in the more volatile constituents and relatively high in vapor phase concentration, while later in the life of the dispenser the rate of diffusion is much lower and the materials which are diffused are more prominently those which have a low evaporation rate. Examples of the prior art which raises this problem or related problems are as follows: U.S. Pat. No. 3,903,022, issued to Ohara et al. on Sept. 2, 1975 (perfume and sublimable substrate which evaporate at similar rates); U.S. Pat. No. 2,927,055, issued to Lanzet on Mar. 1, 1960 (formulation of perfumes having components which ordinarily volatilize at different rates with a novel gelling agent and water in order to level the rate of volatilization of the various perfume components); U.S. Pat. No. 2,710,825, issued to Lazier et al. on June 14, 1955 (teaches the selection of fragrance imparting ingredients of relatively low volatility for a perfume in order to give the diffused material a constant odor character over an extended evaporation period); U.S. Pat. No. 2,905,591, issued to Bulloff on Sept. 22, 1959 (perfume actives and carriers should be selected to have similar vapor pressures); U.S. Pat. No. 4,158,440, issued to Sullivan et al. on June 19, 1979 (components with different volatility are placed in separate dispensing means having compensating dispensing rates); and U.S. Pat. No. 3,679,133, issued to Sekiguchi et al. on July 25, 1972 (perfume is delivered to an evaporation surface under pressure, instead of by wicking, in order to avoid a change in the composition of the diffused material over time).
U.S. Pat. No. 3,821,413, issued to Hellyer, Jr., on June 28, 1974, teaches, particularly in Formulation 1 and the accompanying text and graph, that certain compositions may be formulated in which the proportion of a glycol in the evaporating mixture can be held constant over a period of time. It will be found upon close examination of the reference cited in Hellyer for boiling points that Formulation 1 contains a high proportion of ingredients which have boiling points similar to that of the propylene glycol in the formulation. Hellyer does not teach, however, that the boiling points of the mixture components are relevant to the favorable performance of the composition in maintaining a steady composition during evaporation.
Another problem noted in the prior art relating to dispensers used to diffuse multi-component liquids, and particularly perfumes, is that of wick blockage. When a dispenser of the type employing a wick is used to transpire perfumes over a long period of time, it is found that the rate of perfume delivery often falls off steadily because less volatile components, or the oxidation products of more volatile components, become concentrated in the exposed portion of the wick and block the transfer of fluids within the wick or diffusion of fluids (in vapor form) from the evaporative surface of the dispenser. The prior art discusses this problem and provides various solutions. U.S. Pat. No. 2,529,536, issued to Bjorksten on Nov. 14, 1950, teaches that wick blockage occurs as the components of low volatility in perfume compositions accumulate in the portions of the wick adjacent to the evaporative surface, and teaches that this problem may be alleviated by periodically inverting the wick so that the solvent materials in the reservoir can dissolve the blocking components and thus reverse the wick blockage. The Bulloff reference cited above teaches that perfumes which deposit gums and the like are not favored for use in wick-type dispensers, and further teaches that solid antioxidants should not be used in the perfume, as the solid materials may block the wick. Finally, the Sekiguchi reference cited above suggests that the problem of wick blockage may be alleviated by transferring perfume from the reservoir to the evaporative surface by means other than wicking.
Although the art has made some progress toward the goal of avoiding fractionation of perfumes by providing perfumes made of components with similar volatilities, it will be apparent that in many perfume applications the volatility of the perfume components cannot be so strictly regulated as to eliminate the problem of perfume fractionation.
The present inventors are not aware of any prior art which teaches what properties are needed in a wick-type dispenser system, and particularly in the wick itself, in order to reduce the fractionation of multi-component perfumes. Wicks in the form of sheets have been used in the air humidifying art in order to provide a high level of diffusion of water vapor to the ambient air, but these references do not address the problem of fractionation of a multi-component liquid as it is evaporated because the material to be evaporated is plain water. The relevant references in the humidifier art are U.S. Pat. No. 1,839,357, issued to Thorson et al. on Jan. 5, 1932; and U.S. Pat. No. 1,043,159, issued to Sleeper on Nov. 5, 1912. As with many other references relating to wick structure, these patents teach only that wicking rate is important, or that the ability to wick at all is important, and they do not teach that the amount of liquid material held outside the reservoir in the evaporative surface of the wick should be minimized.
Thus, a first object of the present invention is to provide a dispenser, especially adapted for the diffusion of multi-component liquids, which minimizes the fractionation of the liquid material over time so that the dispensed vapor is relatively constant in concentration and in quality during the useful life of the dispenser.
A second object of the present invention is to provide perfume compositions which are comprised primarily of components having similar levels of volatility, so as to further minimize the problem of uneven distribution of perfume materials during the useful lifetime of a perfume dispenser.
Still another object of the invention is to accomplish the above objectives in a liquid material dispenser which is sufficiently simple and inexpensive to be provided as a single use disposable dispenser.
Still another object of the present invention is to minimize the degradation of the liquid material by air-induced oxidation or polymerization in a wick-type diffusion dispenser.
The improvements in the present invention which satisfy one or more of the above objects of the invention are presented below.